1. Field of the Invention
The invention relates to a target for sputtering used in manufacturing a magnetic recording medium, and to a method for manufacturing a magnetic recording medium using such a target.
2. Background Art
The surface recording density of hard disk media has continued to increase. A medium with a recording density of as high as 70 Gb/in2 has been commercialized. The increased recording density, however, is accompanied by a problem of thermal instability of recording bits. In addition, media noise should be reduced.
To achieve thermal stability and reduced media noise, methods have been tried in which magnetic anisotropy is given to a magnetic layer of a magnetic disk medium. One of the methods forms a texture that is a pattern of convex and concave lines, on a nonmagnetic substrate of the magnetic disk medium, and deposits material on the textured substrate surface to provide magnetic anisotropy in the circumferential direction of the disk.
Some other methods give the magnetic anisotropy to a magnetic layer of the disk by tilting the direction of incident particle beam from the target to the substrate.
Japanese Unexamined Patent Application Publication No. 2001-14664 discloses a method in which a mask having slits with one of various shapes is placed between the target and the substrate. The particles sputtered on the target travel through slits or holes of the mask in which only the particles with a defined tilt (angular direction) reach the substrate, so that planar anisotropy is given to the deposited magnetic layer.
Japanese Unexamined Patent Application Publication No. H7-057237 discloses a method of tilting the incident angle of particles from a target to a substrate. This method is illustrated in FIGS. 9(a) and 9(b) of the present drawings. In the relative positions of a target 31 and a substrate 32 shown in FIG. 9(a), the axes of the two are displaced, keeping the axes in parallel from an original arrangement in which the surfaces of the two disks are parallel and the two axes are coincident, so that the incident angle is tilted from a right angle to an angle φ. In the relative positions shown in FIG. 9(b), the axis of a substrate 32 is tilted from the original arrangement to an angle φ.
A so-called perpendicular recording system is now extensively studied for improving thermal stability and enhancing recording density in which magnetization is perpendicular to the magnetic layer plane. Also being studied is a so-called longitudinal recording system in which magnetization is along the track direction, which is a principal scanning direction. The perpendicular recording system particularly involves a problem of noise from a soft magnetic layer of a recording medium. A possibility has been suggested that this type of noise can be reduced by giving the soft magnetic film anisotropy in a circumferential or radial direction. In a perpendicular recording medium with coercivity higher than 7 kOe, the writing process becomes difficult because the magnetic field intensity generated by the write head is not enough to treat that high coercivity. This problem can be addressed by reducing the coercivity by growing magnetic particles of the recording layer in a tilted direction rather than in a right angle direction, and tilting the major axis of the magnetic particles. Thus, tilting the direction of the incident particle beam to the substrate is useful in a perpendicular recording system as well.
The above-described method, which uses a mask, however, involves a problem that only a fraction of the total of emitted particles reach the substrate by traveling through the slits or holes in the mask. Therefore, the deposition speed of the magnetic film is slow, the performance of the film is not satisfactory, and the deposition process takes a long time. Since the particles trapped on the mask are useless, the efficiency of target utilization is low. Consequently, one target allows the production of only a small number of substrates. Since the particles attached to the mask may become harmful dust, frequent cleaning of the mask is required. These unfavorable facts increase the costs of manufacturing recording media.
In the method, to tilt one of the axes of the target and relative to that of the substrate as shown in prior art FIG. 9(b), nearer portion 32a is situated with a smaller distance between the substrate and the target, while farther portion 32b is situated with a larger distance between them. Thus, a large difference in the distance to the target occurs on the substrate surface. As a result, a homogeneous film cannot be deposited. The efficiency of target utilization is also low. By the method to shift the relative positions of the axes of the target and the substrate as shown in prior art FIG. 9(a), many particles do not enter the substrate and are useless, resulting in a low efficiency of target utilization. In addition, the above-described methods cannot give magnetic anisotropy in a circumferential direction of the substrate.